Intestinal Circulation during Inhalation Anesthesia

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Abstract
The influence of inhalational agents on the intestinal circulation was studied in an isolated loop preparation. Sixty dogs were studied, using 3 intestinal segments from each dog. Selected intestinal segments were pumped with aortic blood at a constant pressure of 100 mm Hg. A mixture of 86Rb and 9-.mu.m spheres labeled with 141Ce was injected into the arterial cannula supplying the intestinal loop, while mesenteric venous blood was collected for activity counting. A very strong and significant correlation was found between Rb clearance and microsphere entrapment (r = 0.97, P < 0.0001), suggesting that the shunting of 9-.mu.m spheres through the intestines reflects the arteriovenous shunting of blood. Nitrous oxide anesthesia was accompanied by a higher vascular resistance (VR), lower flow (F), Rb clearance (Cl-Rb) and microspheres entrapment (Cl-Sph) than pentobarbital anesthesia, indicating that the vascular bed in the intestinal segment was constricted and flow (total and nutritive) decreased. Halothane, enflurane and isoflurane anesthesia were accompanied by a much lower arteriovenous O2 content difference (AVDO2) and O2 uptake than pentobarbital or nitrous oxide. Compared with pentobarbital, enflurance anesthesia was not accompanied by marked differences in VR, F, Cl-Rb and Cl-Sph; halothane at 2 MAC [minimum anesthetic concentrations] decreased VR and increased F and Cl-Rb while isoflurane increased VR and decreased F. .alpha.-Adrenoceptor blockade with phentolamine (1 mg .cntdot. kg-1) abolished isoflurane-induced vasoconstriction, suggesting that the increase in VR was mediated via circulating catecholamines. Decreases in mesenteric blood flow, which are always during inhalation anesthesia, primarily are cuased by the indirect effects of anesthetics medicated through changes in systemic circulation and the CNS.

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